Ichiban Chikakute, Tooi Futari

Ai grew up with a younger sister who was adopted into the family. As they mature, they take on significant roles at their school—Ai serves on the disciplinary committee, while her sister works as a school doctor known for interacting playfully with female students. Ai often reprimands her sister, though it remains unclear whether this is strictly due to adherence to school regulations or other reasons.